Process for simultaneously producing methacrylonitrile and butadiene by vapor-phase catalytic oxidation of mixed butenes

ABSTRACT

This invention provides a process for simultaneously producing methacrylonitrile and butadiene which comprises contacting a mixture of mixed butenes containing isobutene and n-butenes, oxygen and ammonia as the substantial reactants with a catalyst containing as the active component a composition having the empirical formula Fe 10   -  W 1-30  X 0 .01-15 Me 0 .01-5 O 12-143  wherein X is at least one element selected from the group consisting of P, B and Te, and Me represents V and/or Mo in vapor phase.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for simultaneously producingmethacrylonitrile and butadiene by simultaneously effecting ammoxidationand oxidation of mixed butenes containing as the substantial reactantisobutene and n-butenes in vapor phase.

Description of the Prior Art

Heretofore, efficient simultaneous production of methacrylonitrile andbutadiene from mixed butenes containing isobutene and n-butenes bysimultaneously effecting ammoxidation and oxidation in vapor phase usingone and the same catalyst under common reaction conditions has beenconsidered to be difficult due to difference in reactivity betweenisobutene and n-butenes.

A number of processes have recently been proposed for the production ofmethacrylonitrile from olefins by vapor-phase ammoxidation as well asfor the production of butadiene from olefins by vapor phase catalyticoxidation. However, all of these processes involve separative use ofisobutene or n-butenes alone, and there has scarcely been proposed theprocess for simultaneously producing methacrylonitrile and butadiene byvapor-phase oxidation of mixed butenes. Isobutene and n-butene areseparated and purified usually from the B--B fraction (fractioncontaining a mixture of butanes, butenes and butadiene, namely C₄fraction) formed on cracking a petroleum fraction (for example, naphthaor kerosene, or crude oil) or the B--B fraction by-produced inpurification of petroleum, and isobutene, 1-butene, cis-2-butene,trans-2-butene, trans-2-butene and butanes are quite similar in chemicaland physical properties. Accordingly, separation and purification toisolate isobutene or n-butenes with a high purity are not easy andbesides are expensive.

SUMMARY OF THE INVENTION

The major object of this invention is to provide a process forsimultaneously and efficiently producing methacrylonitrile and butadieneby subjecting a mixture of mixed butenes containing isobutene andn-butenes, air or oxygen and ammonia as the substantial reactants tovapor phase oxidation.

The above-mentioned object is realized by the discovery made by thepresent inventors after investigations in various ways that catalystsconsisting of an oxide composition containing iron, tungsten, and atleast one element selected from the group consisting of phosphorus,boron and tellurium and an oxidation composition consisting of theformer composition with oxides of vanadium and/or molybdenum added exertexcellent activities to effect simultaneous production ofmethacrylonitrile and butadiene in high selectivity at high totalconversion.

According to the process of this invention, reactions with a high totalconversion of mixed butenes can be carried out at a relatively lowtemperature and, moreover, simultaneous production of methacrylonitrileand butadiene is feasible under the reaction condition as such at veryhigh conversions. In addition, the methacrylonitrile can surprisingly beobtained in a higher yield than in the production of methacrylonitrilesingly from isobutene. The yield of butadiene in this reaction is alsono less than that in the vapor phase catalytic oxidation of n-butenealone.

Thus, the present invention provides advantageous execution of vaporphase oxidation reaction of mixed butenes containing isobutene andn-butenes by the use of a specific metal oxide catalyst.

Butanes, if any, are inactive in this reaction in the reaction zoneaccording to the process of this invention. The presence of ammonia inthe formation of butadiene produces no substantial effect upon theoxidative dehydrogeneration of n-butene in the reaction zone accordingto the process of this invention.

In these respects, the aforementioned B--B fraction formed on cracking apetroleum fraction such as, for example, naphtha or kerosene or the B--Bfraction by-produced in purification of petroleum as it is, or the spentB--B fraction from separation of butadiene from the former fraction canbe used as the starting material in the present invention. Particularly,the use of the starting material containing 10 to 90 percent ofisobutene and 90 to 10 percent of 1-butene and/or 2-butene issignificantly effective in the process of the present invention.

Generally, what is called spent B--B is included within theabove-mentioned range of composition and contains butanes besides saidcompositions. As mentioned above, however, butanes are inactive underthe reaction conditions of the present invention, and the spent B--B isparticularly suitable as the starting material of the present invention.As mentioned above, the above is accompanied by great advantages thatthe reaction with a high total conversion of the B--B fraction isconducted at a relatively low temperature and simultaneous production ofmethacrylonitrile and butadiene is feasible in a high selectivity. Asseparation and purification of the methacrylonitrile and butadieneobtained by the process of this invention are easily conducted by theuse of difference in boiling point and/or solubility in solvent betweenthe two, the process is commercially very advantageous.

DESCRIPTION OF THE INVENTION

According to the present invention, compositions of the empiricalformula

Fe₁₀ W_(a) X_(b) Me_(c) O_(d)

wherein X is at least one element selected from the group consisting ofP, B and Te, Me is V and/or Mo and the suffixes, a, b, c and d,respectively denoting the atomic ratio, are of values in the ranges: 1 ≦a ≦ 30, 0.01 ≦ b ≦ 15, 0.01 ≦ c ≦ 5 and d is a value corresponding tothe oxides formed from the above-mentioned components by combination andis from 12 to 143 are used as the catalyst useful in effecting thesimultaneous production of methacrylonitrile and butadiene byvapor-phase oxidation of mixed butenes.

The ratio of iron to tungsten in the catalyst of this invention isdefined in terms of atomic ratio to be preferably from 10:1 to 10:30.

The phosphorus, boron or tellurium component is preferably added at aratio from 0.01 to 15 against 10 of the iron component in terms ofatomic ratio. As for the vanadium or molybdenum component, it ispreferable to add at a ratio from 0.01 to 5 against 10 of the ironcomponent.

This is critical for good activity as well as for good selectivity withrespect to the aforementioned reaction and is determined on the basis ofexperiments.

The catalysts having the above-mentioned composition can be produced byany known method, provided that the components are intimately mixed andcombined. Said empirical formula is based upon the analytical value,although exact chemical structure of material constituting the catalystis unknown.

The starting material for providing the iron component of the catalystcan be selected from many members. For example, an oxide of iron in theform of ferrous oxide, ferric oxide or ferro-ferric oxides can be used.Also, those compounds which are finally stabilized as iron oxide afterchemical treatment, calcining treatment or the like may be used. Thesecompounds include salts of iron with a inorganic acid such as ironnitrate and iron chloride, salts of iron with an organic acid such asiron acetate and iron oxalate, etc. The salts can be converted into theoxide by neutralizing them with a basic substance such as aqueousammonia to form iron hydroxide and then calcining said iron hydroxide orby directly calcining them. Besides, hydroxides of iron or metallic ironcan be used. The metallic iron is preferably treated with heated nitricacid. In this case the iron is converted into ferric nitrate. Whateverstarting material is selected, it is critical to intimately mix thematerial with other components.

Any one of water soluble or insoluble tungsten compounds can be used asthe tungsten component source. For example, tungsten trioxide, tungsticacid, amonium paratungstate, ammonium metatungstate, tungsten halides orthe like may be used.

The starting material of the phosphorus or boron component may be of anynature but is most conveniently added in the form of phosphoric acid orboric acid.

Any one of water soluble or insoluble tellurium compounds can be used asthe tellurium component. For example, tellurium dioxide, tellurous acid,telluric acid may be used.

Any one of water soluble or insoluble vanadium compounds can be used asthe vanadium component source. For example, vanadium pentoxide, ammoniummetavanadate, vanadyl oxalate, vanadium halides or the like may be used.

Any one of water soluble or insoluble molybdenum compounds can be usedas the molybdenum component source. For example, molybdenum trioxide,molybdic acid, ammonium molybdate, molybdenum halides or the like may beused.

It is preferable to produce the catalyst composition by intimatelymixing the vanadium or molybdenum component and the tellurium componenttogether with the iron and tungsten components from the beginning.

Alternatively, the catalyst may be produced by initially preparing aniron-tungsten base catalyst followed by adding thereof with othercomponents.

The phosphorus or boron component may either be coexisting in theaqueous solution of the above-mentioned components or may be separatelyadded.

Activity of this catalyst system is increased by heating the same at ahigh temperature. The catalyst material compositon which has beenprepared to provide the desired composition and intimately mixed isdried and then heated at a temperature preferably from about 400° toabout 950°C. for 2 to 48 hours and if required, may be calcined inseveral steps.

The catalyst can show excellent activity even without any carrier, butit may be combined with any suitable carrier. The entire catalyst may beformulated so that it contains 10 to 90 percent by weight of thecatalytic composition. As the carrier may be used silica, alumina,zirconia, silica alumina, silicon carbide, alundum, inorganic silicate,etc.

The other additives such as a binding agent, which serve for improvingthe physical properties of the catalyst, may be optionally added unlessthey impair the activity of the catalyst.

The additives such as a carrier, a binding agent, an extender, etc. canbe optionally added irrespective of their compositions provided thatthey do not remarkably change the characteristics of the catalyst of thepresent invention as described in the above or in the examples below.The catalyst containing these additives sould be also regarded as thecatalyst of the present invention.

The catalyst may be used in a fixed-bed reactor in the form of pellet ormay be used in a fluidized-bed reactor in the form of fine particle.

The reaction conditions for the use of the catalyst of the presentinvention will be explained below.

Any oxygen source may be employed but, for economy, air is convenientlyused. On the other hand, space-time yield in the process of thisinvention can be increased by replacing all or a part of the air byoxygen to increase the concentration of mixed butenes in the reactiongas while maintaining the mixed butenes-oxygen molar ratio in apredetermined range. Under such reaction conditions, yields of thedesired products are considerably lowered with the prior-art catalysts,whereas use of the catalyst of this invention is encountered with almostno reduction of the yields. The enrichment of air with oxygen as setforth above is a favorable means for increasing efficiency in thepurification system and prolonging the life of the catalyst. The processinvolving the oxygen enrichment is preferably conducted in a fluidizedbed-reactor. The molar ratio of oxygen to mixed butenes in the startingreaction gas is preferably in the range between 0.5 and 6.

The formation of methacrylonitrile requires at least 1 mole of ammoniaper mole of isobutene. Lower ratios of ammonia will be unfavorable dueto higher by-production of methacrolein. The amount of ammonia used ispreferably at a molar ratio from 1 to 6 on the basis of isobutene in themixed butenes. Composition of the starting gas is variable dependingupon the composition of mixed butenes and it is preferred to lower theratio of oxygen and ammonia with higher content of 1-butene and to raisethe ratio of oxygen and ammonia with higher content of isobutene.

Addition of steam to the reaction gas, which is often used in the gasphase catalytic oxidation reaction, may also be introduced in theprocess of this invention, if required. Use of water in an amount below5 moles per mole of the mixed butenes may be sufficient in such a case.

The oxygen supplied to the reactor may be supplied in divided streams,some of the oxygen being supplied to the reactor inlet, the remainderbeing supplied into one or more suitable sites in the reactor. Thismethod, which often produces good results, is described in U.S. Pat. No.3,346,617.

Low partial pressure of oxygen will facilitate by-production ofmethacrolein even if partial pressure of ammonia is sufficiently high.In such a case divided supply of oxygen is significantly effective forlowering the production of methacrolein.

The presence of ammonia produces no substantial effect upon theoxidative dehydrogenaton of n-butenes. In some cases, on the contrary,co-existence of ammonia appears to increase the butadiene selectivity.

The temperature at which the reaction is carried out is suitably in therange between about 350° to 500°C. and the reaction when conducted at atemperature from about 380° to 480° C. produces especially good results.From the operational point of view it is preferable to carry out thereaction at and around atmospheric pressure but, if required, reduced orelevated pressure may be applied.

Space velocity, which is an important reaction condition in the vaporphase catalytic reaction using a solid catalyst, is suitably from about5,000 to 100 hr..sup.⁻¹ in the process of this invention. The reactionwhen conducted at a space velocity from about 2,000 to 200 hr.⁻ ¹produces especially good results. The space velocity referred to hereinis the value of gas volume in terms of NTP passing per hour per unitvolume of the catalyst.

Recovery of the desired products methacrylonitrile and butadiene fromthe reaction product may be made by washing the outlet gas from thereactor with cold water or a solvent suitable for extractingmethacrylonitrile and butadiene. Also, any method for recovery which isconventional in the reaction of such a nature may be used.

In carrying out the process of this invention any one of the fixedbed-catalyst, moving bed catalyst and fluidized bed-catalyst equipmentsconventionally used for the gas phase catalytic reaction may beemployed.

The catalysts of this invention generally have little ammoniacombustibility but some of them with a certain composition have thecombustibilities; in the latter case, addition of steam to the reactionsystem may be effective for the inhibition of ammonia combustion.

During the process of this invention 2-butene probably undergoesisomerization, which then produces butadiene. As compared with 1-butene,2-butene is low in reaction rate and slightly inferior in selectivity.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the construction and results of the present invention areshown by the following Examples and Reference Examples:

PREPARATION OF THE CATALYST

Catalyst 1

A catalyst with the empirical formula Fe₁₀ W₂ Te₄ Mo₀.5 Si₃₀ O₉₁ wasprepared as follows:

In a solution composed of 120 ml. of nitric acid (specific gravity 1.38)and 150 ml. of water were dissolved 11.2 g. of electrolytic iron powdersto a solution.

To the iron nitrate solution prepared above were dissolved 10.2 g. ofmetallic tellurium powders to a solution. (I)

In 550 ml. of water were dissolved 10.4 g. of ammonium tungstate and 1.8g. of ammonium molybdate. (II)

As the carrier component were employed 180 g. of silica sol (SiO₂ 20% byweight). (III)

To a mixture of (I) and (III) was added (II).

The resulting mixture was heated under stirring to dryness. The driedmatter, pulverized, was calcined at 200°C. for 2 hours and subsequentlyat 400°C. for 2 hours, followed by addition of water and blending. Theblended matter was formed into pellets, which was dried at 130°C. for 16hours and then calcined at 700°C. for 4 hours.

Catalyst 2

A catalyst with the empirical formula Fe₁₀ W₁₀ Te₅ Mo₁ Si₅₀ O₁₅₈ wasprepared in accordance with the method for Catalyst 1.

Catalyst 3

A catalyst with the empirical formula Fe₁₀ W₂₅ Te₁₀ Mo₂ Si₁₀₀ O₃₁₆ wasprepared in accordance with the method for Catalyst 1 except thatconditions for final calcining were at 600°C. for 4 hours.

Catalyst 4

A catalyst with the empirical formula Fe₁₀ W₁₀ Te₂ P₂ Mo₁ Si₅₀ O₁₅₇ wasprepared in accordance with the method for Catalyst 1 except thatconditions for final calcining were at 650°C. for 4 hours

Catalyst 5

A catalyst with the empirical formula Fe₁₀ W₂₅ Te₁₀ V₁ Si₅₀ O₂₁₃ wasprepared in accordance with the method for Catalyst 1 except thatconditions for final calcining were at 600°C. for 4 hours.

Catalyst 6

A catalyst with the empirical formula Fe₁₀ W₂₀ P₂ Mo₁ Si₃₀ O₁₄₃ wasprepared in accordance with the method for Catalyst 1 except that Pcomponent was added instead of Te component and phosphoric acid was usedas the starting material for P component.

The conditions for final calcining of the catalyst were at 600°C. for 4hours.

Catalyst 7

A catalyst with the empirical formula Fe₁₀ W₂₀ B₂ Mo₁ Si₃₀ O₁₄₁ wasprepared in accordance with the method for Catalyst 1 except that Bcomponent was added instead of Te component and boric acid was used asthe starting material for B component.

The conditions for final calcining of the catalyst were at 600°C. for 4hours.

METHODS AND RESULTS OF THE TEST

The method of testing the catalyst was as follows:

1. Composition of the mixed butenes starting materials.

A. isobutene 52%, 1-butene 48%.

B. butane 12%, isobutene 46%, 1-butene 28%, 2-butene 14%.

The starting materials used are cited in the table 1 and table 2 as A,B.

2. reaction procedures

2-1. Reaction in a fixed bed

Reactions were performed in a fixed bed using Catalysts 1-7.

A U-shaped reactor, 16 mm.φ in inner diameter and 500 mm. in length, wasfilled with 20 ml. of the catalyst which formed into pellets 2 mm.φ×2mm.φ. The reactor was heated in a salt bath of an equal-amount mixtureof sodium nitrite and potassium nitrate to maintain the same at apredetermined reaction temperature. The reactant gas was passed throughthe reactor thus prepared at a rate of 10 liters per hour (in term ofNTP). The reaction pressure was atmospheric.

Composition of the supplied gas was as follows:

air/mixed butenes = 16 (molar ratio)

NH₃ /mixed butenes = 0.8 (molar ratio)

The bath temperature was successively changed and reaction was continuedfor 30 min. to 1 hour at a given temperature.

The reaction gas was analyzed by gas chromatography. Data of thereactions that have given the best results are shown in Table 1.

In the Reference Examples, reactions were performed with 1-butene orisobutene alone under the same conditions as the Examples, the resultsof which are also shown in Table 1.

2--2. Reaction in a fluidized-bed

Catalysts 3 and 5 were subjected to a spray drying in accordance withthe conventional method and subsequently to the same calcining treatmentas mentioned above to produce a fluidized catalyst, and then reactionswere performed in a fluidized bed using the fluidized catalyst.

The reaction apparatus used was 2 in. in inner diameter and 1 m. inheight. It was filled with the catalyst 10-100μ in particle size for themost part in such a manner that space velocity was 500 hr..sup.⁻¹

The supplied gas prepared so as to give the below-mentioned compositonwas passed through the reactor at a linear velocity of 15 cm./sec.

air/mixed butenes = 16 (molar ratio)

ammonia/mixed butenes = 0.8 (molar ratio)

Analysis of the reaction gas was made by gas chromatography.

Results of the reactions are shown in Table 2.

The total conversion respectively of isobutene and n-butenes (1-buteneand 2-butene) in the mixed butenes and conversion respectivey tomethacrylonitrile and butadiene as referred to herein are defined asfollows: ##EQU1##

                                      TABLE 1                                     __________________________________________________________________________                                 Conditions for                                                   Composition  the final cal-                                                   of the catalyst                                                                            cining of the                                                                         Mixed                                                    (atomic ratio)                                                __________________________________________________________________________     butenes                                                                            Cata-                  Temp.                                                                             Hour                                                                              starting                                 Example                                                                             lyst                                                                              Fe W  X   Me   Si  (°C)                                                                       (hrs)                                                                             material                                 __________________________________________________________________________    1     1   10 2  Te 4                                                                              Mo0.5                                                                              30  700 4   A                                        2     2   10 10 Te 5                                                                              Mo 1 50  700 4   A                                        3     3   10 25 Te10                                                                              Mo 2 100 600 4   A                                        4     3   10 25 Te10                                                                              Mo 2 100 600 4   B                                        5     4   10 10 Te 2                                                                              Mo 50                                                                              650 4   A                                                            P 2                                                           6     5   10 25 Te10                                                                              V 1  50  600 4   B                                        7     6   10 20 P 2 Mo 1 30  600 4   A                                        8     7   10 20 B 2 Mo 1 30  600 4   A                                        Reference                                                                     Example                                                                       1     2   10 10 Te 5                                                                              Mo 1 50  700 4   --                                       2     5   10 25 Te10                                                                              V 1  50  600 4   --                                       3     7   10 20 B 2 Mo 1 30  600 4   --                                       4     2   10 10 Te 5                                                                              Mo 1 50  700 4   --   .].                                 __________________________________________________________________________

                                      TABLE 1-continued                           __________________________________________________________________________               Total Conver-                                                      Optimum    sion (%) of                                                                            Conversion (%)                                                                         Selectivity                                      reaction       1-   to       (%)                                                    tempera-                                                                           Iso-                                                                              butene,                                                                            Metha-   Metha-                                                 ture butene                                                                            2-   crylo-                                                                             Buta-                                                                             crylo-                                                                             Buta-                                       Example                                                                             (°C)                                                                            butene                                                                             nitrile                                                                            diene                                                                             nitrile                                                                            diene                                       __________________________________________________________________________    1     400  98  95   71   75  72   79                                          2     410  98  94   79   81  81   86                                          3     410  97  92   83   82  85   89                                          4     410  93  88   79   76  85   86                                          5     410  98  92   72   74  73   80                                          6     400  96  92   69   72  72   78                                          7     400  95  92   68   71  72   78                                          8     400  96  93   68   72  71   76                                          Reference                                                                     Example                                                                       1     410  99  --   77   --  78   --                                          2     400  98  --   67   --  68   --                                          3     400  98  --   64   --  65   --                                          4     410  --  97   --   81  --   83                                          __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                                 Conditions for                                                                the final cal-                                                  Compositions  cining of the                                                                         Mixed                                                   of the catalyst                                                                             catalyst                                                                              butenes                                  Cata-          (atomic ratio)                                                                              Temp.                                                                             Hour                                                                              starting                                 Example                                                                            lyst                                                                              Fe W  X    Me   Si  (°C)                                                                       (hrs)                                                                             material                                 __________________________________________________________________________    9    3   10 25 Te10 Mo 2 100 600 4   A                                        10   5   10 10 Te 2 Mo 1  50 600 4   A                                                       P 2                                                            __________________________________________________________________________

                                      Table 2                                     __________________________________________________________________________               Total conver-                                                      Optimum    sion (%) of                                                                            Conversion (%)                                                                         Selectivity                                      reaction       1-   to       (%)                                                    tempera-                                                                           Iso-                                                                              butene,                                                                            Metha-   Metha-                                                 ture butene                                                                            2-   crylo-                                                                             Buta-                                                                             crylo-                                                                             Buta-                                       Example                                                                             (°C)                                                                            butene                                                                             nitrile                                                                            diene                                                                             nitrile                                                                            diene                                       __________________________________________________________________________    9     420  95  90   80   79  84   88                                          10    400  95  92   70   71  74   77                                          __________________________________________________________________________

We claim:
 1. Process for simultaneously producing methacrylonitrile andbutadiene which comprises contacting a mixture of butenes consistingessentially of isobutene and n-butene, oxygen and ammonia in vapor phaseat a temperature of from about 350° to 500°C with a catalyst consistingof an oxide composition containing the elements in atomic ratioaccording to the formulaFe₁₀ W_(a) X_(b) Me_(c) O_(d) wherein X is atleast one element selected from the group consisting of phosphorus,boron and tellurium; Me is at least one element selected from the groupconsisting of vanadium and molybdenum; the subscripts denote atomicratio and have the values: a = 1-30 b = 0.01-15 c = 0.01-5;and d is avalue corresponding to the oxides formed from the above components bycombination and is from 12 to 143, wherein said catalyst is produced byintimately mixing at least one compound of each of the respectiveelements in an aqueous system, heating to dryness and calcining at atemperature from about 400° to about 950°C for 2 to 48 hours.
 2. Theprocess of claim 1, wherein said mixtures of butenes consistsessentially of from about 10 to about 90 percent isobutene and about 10to about 90 percent 1-butene and/or 2-butene; the oxygen/mixed butenemolar ratio is from 0.5/1 to 6/1; and the ammonia/isobutene molar ratiois from 1/1 to 6/1.
 3. Process according to claim 1 wherein spacevelocity of said starting mixture is within the range from 5,000 to 100hr..sup.⁻¹.
 4. Process according to claim 1 wherein said catalyst is incombination with silica carrier in a portion from 10 to 90 percent byweight.